1. Field of the Invention
The present invention relates to a storage battery which comprises a battery case used as one polarity terminal and having an opening, a port-sealing body used as other polarity terminal, for sealing the opening, and an electrode body installed into the battery case and having a current collecting body connected to at least one of end portions of positive/negative electrodes and a method of fabricating the same and, more particularly, an improvement of a current collecting structure of a lead portion for connecting the current collecting body connected to at least one of the positive/negative electrodes and the port-sealing body of a solution battery such as alkaline cell and lead cell and a welding method therefor.
2. Description of the Related Art
In general, the alkaline storage battery such as the nickel-hydrogen storage battery, the nickel-cadmium storage battery, or the like are constructed by interposing the separator between the positive electrode and the negative electrode, then winding them spirally, then connecting the current collecting body to the end portion of the positive electrode or the negative electrode to form the electrode body, then installing the electrode body into the metal battery case, then welding the lead portion extended from the current collecting body to the port- sealing body, and then fitting the port-sealing body to the opening portion of the battery case via the insulation gasket to seal tightly the battery case.
In case such alkaline storage battery is employed in the application such as the electric-powered tool, the electric. vehicle, etc. in which charging/discharging operations are performed at a high rate, the electric resistance of the lead portion which connects the current collecting body and the port-sealing body affects largely the battery characteristic. Thus, if the electric resistance of the lead portion is large,. there is such a problem that, when the discharge is performed by the large current, the voltage drop due to the electric resistance of the lead portion is caused to lower the battery voltage. Therefore, in Japanese Patent No. 2762599, it has been proposed to reduce the electric resistance of the lead portion by using plural sheets of current collecting parts to construct the lead portion or increasing the thickness of the current collecting parts.
Meanwhile, in case a plurality of current collecting parts constituting the lead portion are employed, such problems are caused that the welding to the port-sealing becomes difficult since not only the number of parts is increased but also the lead portion lacks the flexibility and that productivity is deteriorated since it becomes difficult to fold the lead portion when the port-sealing body is caulked to the opening portion of the battery case to seal. Also, in case the thickness of the current collecting parts constituting the lead portion is increased, such problems are caused that weldability to the port-sealing body is deteriorated since the reactive current is increased in the welding current for the resistance welding and that the productivity is deteriorated since it becomes difficult to fold the lead portion when the port-sealing body is caulked to the opening portion of the battery case to seal.
In contrast, in case the lead portion is welded to the port-sealing body, first the lead portion is resistance-welded to the port-sealing body while pushing the welding electrode against the side surface of the lead portion after the port-sealing body is positioned in the neighborhood of the lead portion that stands perpendicularly from the current collecting body. After this, the port-sealing body is fitted into the opening portion of the battery case by folding the lead portion and then the edge portion of the opening portion is caulked to seal tightly. Normally, if the lead portion that is thick and short is employed, its specific resistance can be reduced and thus the internal resistance of the battery can be lowered.
However, as described above, in order to fit the port-sealing body into the opening portion of the battery case after the lead portion is welded to the port-sealing body, the port-sealing body must be fitted into the opening portion of the battery case by using the longer lead portion so as to fold the lead portion at the time of sealing. Therefore, a length that exceeds at least a radius of the electrode body is needed as the length of the lead portion, and also the thin and long lead portion must be employed such that the lead portion can be folded. Thus, there is caused the problem that, since the specific resistance of the lead portion is increased, the internal resistance of the battery is increased.
Therefore, the connecting method of reducing the internal resistance of the battery by reducing the current collecting route has been proposed in unexamined Japanese Patent Publication (JP-A) 10-261397, for example. According to this method, the electrode body is installed into the battery case, then the opening portion of the battery case is sealed tightly by the port-sealing body in the situation that the lead portion welded to the current collecting body is brought into contact with the lower surface of the port-sealing body, and then the contact portion between the lead portion and the port-sealing body are welded by flowing current between the battery case and the port-sealing body.
Accordingly, it is possible to install easily the port-sealing body into the opening portion of the battery case if the lead portion is short, and it is possible to reduce the internal resistance of the battery by reducing the current collecting distance. Also, since there is no need to fold the lead portion in sealing the opening, it is possible to use the thick lead portion and also it is possible to reduce the internal resistance of the battery.
However, in the connecting method proposed in JP-A 10-261397, in case the height of the electrode body installed in the battery case is varied, the situation may occur wherein the contact portion between the port-sealing body and the lead portion cannot be surely formed. Thus, the problem arises that the welding portion cannot be firmly formed. Also, the strength and the quality of the welding spot after welding is deteriorated only by bringing the lead portion into contact with the port-sealing body, and in some cases yield of the product is degraded.
Therefore, the present invention has been made to overcome the above problems, and it is a first object of the present invention to obtain a storage battery which is excellent in high-rate discharge performance by using lead parts which can weld a port-sealing body and a current collecting body without fail even if its thickness is large and its length is small. Also, it is a second object of the present invention to provide a welding method capable of welding the lead portion and the port-sealing body or the lead portion and the current collecting body by using such lead parts to connect them without fail.
In order to achieve the above first object, the battery of the present invention the lead portion for connecting the port-sealing body and the current collecting body is constructed by the cylindrical body having the hollow portion, then this cylindrical body having the hollow portion is provided between the port-sealing body and the current collecting body, and then the port-sealing body and the current collecting body are welded to the lead portion formed of the cylindrical body.
If the port-sealing body and the current collecting body are welded to the lead portion having the hollow portion and formed of the cylindrical body, the current route in supplying the current is divided into two routes from the current collecting body to the port-sealing body (otherwise, from the port-sealing body to the current collecting body) along the peripheral side wall of the cylindrical body to flow the current. Hence, the current collecting distance of the lead portion becomes the semicircle of the cylindrical body and thus the voltage drop in the lead portion can be reduced by half. As a result, since there is no necessity to increase the thickness of the base material of the cylindrical body acting as the lead portion, the welding between the lead portion and the port-sealing body or the current collecting body is made easy and the operation for sealing the opening of the port-sealing body by caulking the opening portion of the battery case is made easy. Thus, the fabrication of the storage battery of this type becomes easy.
Further according to welding by flowing a large current. through electrolyte under high pressure, it is able to weld very easily, reliably and with high quality. And confirm and high connecting strength of welding portions can be obtained.
Also, in order to achieve the above second object,. the storage battery fabricating method of the present invention comprising the arranging step of arranging the port-sealing body in the opening portion of the battery case such that the current collecting body is brought into contact with the port-sealing body via a lead portion that connects electrically the current collecting body and the port-sealing body, and the welding step of welding the lead portion to any one of the port-sealing body and the current collecting body by flowing a current between the battery case and the port-sealing body while pressurizing the battery case and the port-sealing body.
At this time, in order to enhance the strength of the welded portion by the resistance welding, the current value of the welding current as well as the welding force applied to the welding spot are important factors. If the welding current is supplied to the welding spot, the metal of the contact portion is fused by Joule""s heat at the welding spot to weld. In this case, if the welding spot is not pressurized, a phenomenon that the fused metal scatters occurs to thus generate so-called xe2x80x9cweld dustxe2x80x9d. This is one of causes of short-circuit of the battery. Also, if the welding spot is not pressurized, the internal defect occurs at the welding spot to lower the weld strength.
However, in the welding method proposed in above JP-A 10-261397, since the welding is carried out after the opening portion of the battery case is tightly sealed by the port-sealing body, such port-sealing body is fixed. Thus, since the welding force cannot be applied to the welding spot in the welding, there is the problem that xe2x80x9cweld dustxe2x80x9d and the internal defect are caused.
However, in the present invention, the port-sealing body is arranged in the opening portion of the battery case so as to bring the port-sealing body into contact with the current collecting body via the lead portion, and then the welding current is supplied between the battery case and the port-sealing body. Therefore, it is possible to pressurize the contact portion in welding. Accordingly, the lead portion can be welded well to any one of the port-sealing body and the current collecting body without generation of the xe2x80x9cweld dustxe2x80x9d. As a result, if the lead portion has a mere length to connect the port-sealing body and the current collecting body, such lead portion can be welded to the port-sealing body or the current collecting body.
Also, if the lead portion is constructed by the cylindrical body having the hollow portion, the current route in supplying the current is divided into two routes from the current collecting body to the port-sealing body (otherwise, from the port-sealing body to the current collecting body) along the peripheral side wall of the cylindrical body to flow the current. Therefore, the voltage drop in the lead portion can be reduced by half rather than the case where a sheet of lead plate is employed. For this reason, since there is no necessity to increase the thickness of the base material of the cylindrical body acting as the lead portion, the welding between the lead portion and the port-sealing body or the current collecting body is made easy and the operation for sealing the opening of the port-sealing body by caulking the opening portion of the battery case is made easy. Thus, the fabrication of the storage battery of this type becomes easy.
Further by having a structure that outer ends of the peripheral side surface of the lead portion are located inner than those of the bottom surface of the sealing body, a current path is divided into two paths from the port-sealing body to the current collecting body along a peripheral side surface of the cylindrical body, and current path can be shortened. Also, since the peripheral side surface of the cylindrical body can be welded previously to the current collecting body or the port-sealing body by providing the first welding step of welding previously the cylindrical body to the current collecting body or the first welding step of welding previously the cylindrical body to the port-sealing body, movement of the cylindrical body in the second welding step performed later can be prevented. Accordingly, it is ready to weld the cylindrical body to the port-sealing body or to weld the cylindrical body to the current collecting body in the second welding step.
In addition, if the peripheral side surface of the cylindrical body can be welded previously to the current collecting body or the port-sealing body, the welding current can be concentrated into the contact portion between the peripheral side surface of the cylindrical body and the port-sealing body or the contact portion between the peripheral side surface of the cylindrical body and the current collecting body in the second welding step performed later. As a result, the excellent welded portion can be formed and thus the welded portion having the excellent weld strength can be formed.
Then, if the current is supplied while pressurizing the port-sealing body and the battery case in the second welding step, it is possible to form the contact spot between the peripheral side surface of the cylindrical body and the port-sealing body or the current collecting body even if the height dimension of the electrode body is varied or the welding position of the cylindrical body welded previously to the current collecting body or the port-sealing body is varied.
By carrying a welding step while pressurizing the current collecting body and the lead portion, the current collecting body and the lead portion are associated with each other in an instant of melting, it is easy to weld the current collecting body and the lead portion. Further inner defect such as voids can be suppressed.
Accordingly, not only generation of xe2x80x9cweld dustxe2x80x9d acting as a cause to generate the internal short-circuit and generation of the internal defect to cause the reduction of the weld strength can be suppressed, but also the welded portion that has an excellent weld strength can be formed. Thus, the resistance value in the welding portion can be reduced. As a result, the storage battery in which no short-circuit is generated and the internal resistance is small can be obtained.
In this case, if the opening portion of the battery case is sealed tightly by the port-sealing body by supplying the current between the battery case and the port-sealing body while pressurizing the lead portion between the port-sealing body and the current collecting body after the welding step or the second welding step is carried out, generation of the xe2x80x9cweld dustxe2x80x9d can be suppressed without fail and also the welded portion that has no internal defect and has the excellent weld strength can be formed. Otherwise, if the welding step or the second welding step is carried out by not only pressurizing the lead portion between the port-sealing body and the current collecting body while crashing the annular groove formed on the upper portion of the battery case but also supplying the current between the battery case and the port-sealing body after the port-sealing portion is formed around the port-sealing body by sealing tightly the opening portion of the battery case by the port-sealing body, generation of the xe2x80x9cweld dustxe2x80x9d can be suppressed without fail and also the welded portion that has no internal defect and has the excellent weld strength can be formed.
Then, any shape may be employed as the cylindrical body constituting the lead portion if such shape enables to divide the current route into two routes in supplying the current and such shape is easily crashed by the pressurizing force in the sealing step. In this case, the cylindrical body having the sectional shape of the circular shape, the elliptic shape, or the polygonal shape is preferable because it can satisfy these conditions. Therefore, the sectional shape of the cylindrical body has a shape that is obtained by crashing the circular shape, the elliptic shape, or the polygonal shape by the pressurizing force in the sealing step.
Further, if the notched portions extending in the axial direction are provided on both edges of the cylindrical body, the cylindrical body is easily crashed by the pressurizing force in the sealing step along the notched portions. Also, if at least one of both edges of the cylindrical body is cut off obliquely, the welding electrode rod can be positioned perpendicularly to the exposed surface since a part of the inner peripheral surface of the cylindrical body on both ends is exposed by this cutting-off. Accordingly, the cylindrical body can be welded previously to the port-sealing body or the current collecting body by using a simple structure obtained by cutting off the end portions of the cylindrical body obliquely. Thus, since the current collecting distance is a semicircle distance from the welded spot on the current collecting body to the welded spot on the port-sealing body, such current collecting distance can be reduced.
Moreover, if the cylindrical body has flat plate blade portions extending from the peripheral side surface to both sides, to weld previously such cylindrical body to the port-sealing body or the current collecting body is made easy. Also, if the projection portions are provided to the lower surface of the port-sealing body or if the projection portions are provided to the peripheral side surface of the cylindrical body contacting to the upper surface of the port-sealing body, the welded portion having the larger weld strength can be formed since the current can be concentrated into the projection portions. Also, if the blade portions are formed by extending a part of the peripheral side wall of the cylindrical body, formation of the blade portions becomes easy.
Further according to providing projection portions on at least one of a lower surface of the electrode body and inner surface of the casing, by concentrating the current into the projection portions, the lower surface of the electrode body and inner surface of the casing can be welded each other very easily and confirmly, and connection with confirm and low resistance can be obtained.